KAMPALA, Uganda -- Uganda has started vaccinating health workers against Ebola in a border district near the outbreak in Congo, where the highly infectious viral disease has killed 189 people.

The inoculations, using an experimental vaccine, began on Wednesday and are part of a wider Ebola prevention plan in a country that has faced multiple Ebola outbreaks since 2000.

In recent months Ebola cases have been confirmed near the heavily travelled border between Uganda and Congo, where 270 cases have been reported in the country's northeast since August.

The vaccinations are crucial to stemming transmission "in a highly endemic belt for hemorrhagic fevers," said Anthony Mbonye, a professor of health sciences at Uganda's Makerere University.

Twice-weekly market days - during which some 10,000 Congolese cross into Uganda - have put Uganda at high risk, according to local health officials. They say unofficial border crossings also are a cause for concern.

Health workers are usually among the first to be infected in an Ebola outbreak.

The death from Ebola of a young Ugandan physician in 2000, one of more than 200 people killed in that outbreak, sparked a national outpouring of grief and helped spread awareness of how Ebola is transmitted.

The ongoing Uganda vaccinations targeting frontline health workers will be carried out in five districts along the border with Congo. Several studies have shown that the vaccine is safe and protects against the Ebola virus, the World Health Organization said in a statement.

The vaccine, although subject to more scientific research and is still not yet licensed, is "being used on a compassionate basis, to protect persons at highest risk of the Ebola outbreak," the statement said.

In Congo, where thousands of people have been given the experimental Ebola vaccine, a worrying number of vaccinated health workers have been infected.

The WHO said last month that Congo's outbreak does not yet warrant being declared a global emergency but called for an "intensified" response. Dozens more have died since then, according to a tally reported by Congo's health ministry.

For Congolese health workers, combating the virus has proved a challenge in a densely populated region that is roamed by armed groups.

Investigators believe that the first victim of Ebola in any outbreak acquires the virus after coming into contact with a "reservoir" animal, say an infected bat or monkey.

Ebola was first reported in Congo in 1976 and is named for the river where it was recognized.

The Ebola virus is spread through direct contact with the fluids of an infected person, or objects that have been contaminated with infected secretions.